标题： 测试表面亮度涨落法在半人马座A星系群矮椭球星系中的应用 显示英文标题

标题： Testing the Surface Brightness Fluctuations Method for Dwarf Elliptical Galaxies in the Centaurus A Group

摘要： 我们获得了覆盖天鹤A（Centaurus A，Cen A）星系群区域的施密特底片上先前确认的5个矮椭球星系的深B和R波段CCD测光数据。通过对R波段CCD图像进行傅里叶分析，我们确定了每个恒星系统的表面亮度涨落（SBF）星等。所有星等值相似，表明这些低表面亮度星系大约处于相同距离，与假设的SBF零点无关。为两个矮星系ESO269-066和ESO384-016获取了长狭缝光谱以推导其红移值。速度测量明确地将它们识别为天鹤A星系群成员。光谱的年龄-金属丰度分析显示，在这两种情况下都存在潜在的老年且金属贫乏的恒星群体。结合测光和光谱结果，我们发现有强有力的证据表明，所有矮椭球星系确实是天鹤A星系群的成员。基于已发表的天鹤A星系群两个主要星系NGC5128和NGC5253的精确距离，我们采用3.96 Mpc的平均星系群距离来校准表观涨落星等。矮椭球星系的绝对SBF星等\bar{M}_R 与颜色(B-R)\(_0\) 呈良好相关性，这允许在颜色范围0.8<(B-R)\(_0\)<1.5内对SBF方法进行校准。其中一个矮星系ESO219-010位于天鹤A星系群核心后方约4.8 Mpc处，而其余四个则恢复了用于校准的平均星系群距离3.96 Mpc。该星系群的深度仅为0.5 Mpc，这表明天鹤A星系群是一个空间上相对孤立的星系聚合体，与附近的雕塑家（Sculptor）星系群形成对比。 显示英文摘要

摘要： We have obtained deep B and R-band CCD photometry for 5 dE galaxies that were previously identified on Schmidt films covering the Cen A group region. From a Fourier analysis of the R-band CCD images we determined the surface brightness fluctuation (SBF) magnitude for each stellar system. All magnitudes are similar and suggest that these low surface brightness galaxies lie approximately at the same distance, regardless of the assumed SBF zero point. Long-slit spectra have been acquired to derive redshifts for two of the dwarfs, ESO269-066 and ESO384-016. The velocities identify them unambiguously as Cen A group members. An age - metallicity analysis of the spectra reveals an underlying old and metal-poor stellar population in both cases. Combining photometric and spectroscopic results we find strong evidence that indeed all dEs are Cen A group members. Based on accurate distances published for the two main Cen A group galaxies NGC5128 and NGC5253, we adopted a mean group distance of 3.96 Mpc to calibrate the apparent fluctuation magnitudes. The resulting absolute SBF magnitudes \bar{M}_R of the dEs correlate with the colours (B-R)_0 as good agreement allows a calibration of the SBF method for dEs in the colour range 0.8<(B-R)_0<1.5. One of the dwarfs, ESO219-010, is located slightly behind the core of the Cen A group at 4.8 Mpc, while the remaining four recover the mean group distance of 3.96 Mpc that was put into the calibration. The depth of the group is only 0.5 Mpc which identifies the Cen A group as a spatially well isolated galaxy aggregate, in contrast to the nearby Sculptor group.